Curious, my Machform login shows a "Forgot Password" link....(https://forms.murraywebs.biz/ as an example) so don't know why yours does not.
My guess is that the forgot password is a feature introduced in newer versions than your own. Try updating to the latest (V10). You don't need to be in Machform to upgrade. That's the only thing I can think of.
Appnitro (if you submit a support ticket to them) could possibly reset it for you). You need to log in to your Appnitro customer area to submit support requests. Note their support hours are just their standard operating hours, 9 to 5 M-F - their time zone GMT +7:00 give or take one hour for daylight saving.